This is a key-value map that will let you write and retrieve objects to and from the saved state.
These values will persist after the process is killed by the system
and remain available via the same object.

LiveData can have null as a valid value. If the
initialValue is null and the data does not already exist in the
SavedStateHandle, the value of the returned LiveData will be set to
null and observers will be notified. You can call getLiveData(String) if
you want to avoid dispatching null to observers.